Heterophase adhesive compositions containing chlorosulfonated polyethylene for metal-selenium composites

ABSTRACT

A xerographic member which comprises a conductive substrate having thereon an interfacial barrier layer in a thickness of about 0.5 to 3.0 microns. The barrier layer comprises a polymer blend or mixture of a polycarbonate, a polyether-ester-urethane, and a chlorosulfonated polyethylene and is overcoated with a photoconductive layer about 10 to 200 microns in thickness.

United States Patent 11 1 Lee [ HETEROPI-IASE ADHESIVE COMPOSITIONSCONTAINING CHLOROSULFONATED POLYETHYLENE FOR METAL-SELENIUM COMPOSITES[75] lnventor: Lieng Huang Lee, Webster, NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Aug. 17, 1973 {21] Appl. No.: 389,283

52 us. (:1. 1. 96/15; 117/200; ll7/2l8 51 1m. 01 1. G03g 5/04 58 Fieldof Search 96/].5; 117/200. 218

[56] References Cited UNITED STATES PATENTS 3,7l3.82l l/l973 Angelini96/l.5

[ June 24, 1975 3/l973 Goffe ..96/|.5 6/l973 Merrill ll7/2l8 OTHERPUBLICATIONS Organic Coatings for Electronics" Products Finishing, July,l97l, pp. 74-80, Licari and Brands.

Primary Examiner-Norman G. Torchin Assistant E.raminerjudson R.Hightower 12 Claims, 1 Drawing Figure HETEROPHASE ADHESIVE COMPOSITIONSCONTAINING CHLOROSULFONATED POLYETIIYLENE FOR METAL-SELENIUM COMPOSITESBACKGROUND OF THE INVENTION This invention relates in general toxerography, and in particular. to an improved interfacial layer for axcrographic member.

In the art of xerography, a xerographic plate containing aphotoconducting insulating layer is first given a uniform electrostaticcharge in order to sensitize its surface. The plate is then exposed toan image of activating electromagnetic radiation, such as light, whichselectively dissipates the charge in the illuminated areas of thephotoconductive insulator while leaving behind a latent electrostaticimage in the nonilluminated areas. The latent electrostatic image may bedeveloped and made visible by depositing finely divided electroscopicmarking particles in the surface of the photoconductive layer. Thisconcept was originally described by Carlson in US. Pat. No. 2,297,691and is further amplified and described by' many related patents in thefield.

conventionally, a xerographic member or plate normally includes aconductive base or support which is generally characterized by theability to conduct electricity for charging or sensitization of acomposite member and to accommodate the release of electric charge uponexposure of the member to activating radiation such as light. Generally,this conductive support must have a specific resistivity of less thanabout l ohm-cm, and usually less than about IO ohm-cm. The conductivesupport should also have sufficient structural strength to providemechanical support for the photosensitive member thus making it readilyadaptable for xerographic machines suitable for commercial use.

The conventional xerographic plate normally has a photoconductiveinsulating layer overlaying a conductive support. The photoconductor maycomprise any suitable material known in the art. For example, vitreousselenium, or selenium modified with varying amounts of arsenic is oneexample of one suitable reusable photoconductor which has wide use incommercial xcrography. In general, the photoconductive layer must have aspecific resistivity greater than about lO' ohmcm in the absence ofillumination and preferably at least ohm-cm. The resistivity should dropat least several orders of magnitude in the presence of activatingradiation or light. In general. the photoconductive layer should supportan electrical potential of at least about [00 volts in the absence ofradiation and may vary in thickness from about It) to 200 microns.

A plate having the above configuration, normally under dark roomconditions, exhibits a reduction in potential or voltage leak in theabsence or activating radiation which is known as dark decay" andexhibits a variation in electrical performance upon repetitive cyclingwhich is described in the art as fatigue. The problems of dark decay"and fatigue" are well known in the art and have been remedied by theincorporation in the plate structure of a barrier layer which comprisesa thin dielectric material only a fraction of the thickness of thephotoconductive layer. This barrier or interfacial layer isinter-disposed between the conductive substrate and the photoconductiveinsulating layer. US. Pat. No. 2,90l.348 to Dessauer et al contemplatessuch a layer and suggests the use of a thin layer or film of aluminumoxide in a thickness range of about 25 to 200 angstroms; or aninsulating resin layer, such as polystyrene, in the order of about 0.]to 2 microns in thicknessv These barrier layers function to allow thephotoconductive layer to support a charge of high field strength withminimum charge dissipation in the absence of illumination. Whenactivated by illumi nation, the photoconductive layer becomesconductive, thereby causing a migration of the appropriate chargesthrough said photoconductive layer and the appropriate dissipation ofcharge in the radiation or illumination struck areas.

In addition to the electrical requirements of a barrier layer, it isalso necessary that such a layer meets certain requirements with regardto mechanical properties such as adhesion to the photoreceptor andoverall flexibility. For example, when using a flexible photoreceptor,such as a continuous belt, both the photoconductor and interface must beproperly matched so as to have the required electrical characteristicsand mechanical stability. It has been demonstrated that after a greatdeal of flexing, many interfaces tend to spall or crack, resulting inthe flaking off or spalling of sections of the photoreceptor renderingit no longer suitable for use in xcrography. Therefore, there is acontinuing need for improved barrier layers which meet both the requiredelectrical characteristics and mechanical properties for use inapplications in which a flexible xerographic member or belt is used.

OBJECTS OF THE INVENTION It is, therefore, an object of the invention toprovide a new and improved photoreceptor barrier layer which overcomesthe above noted disadvantages.

It is another object of this invention to provide a photoreceptivemember which exhibits improved electrical characteristics and mechanicalproperties.

It is another object of this invention to provide an improvedinterfacial barrier layer.

SUMMARY OF THE INVENTION The foregoing objects and others areaccomplished in accordance with this invention by providing aphotoconductive member which exhibits improved electricalcharacteristics and mechanical properties, and which includes a novelinterfacial barrier layer which comprises a heterophase adhesivecomposition containing a polycarbonate, a polyether-ester-urethane, anda chlorosulfonated polyethylene. More specifically, the interfaciallayer comprises either a polymer blend or mixture of a polycarbonate, apolyether-esterurethane, and a chlorosulfonated polyethylene which issandwiched between a photoconductive insulating layer and a supportingsubstrate. One of the advantages of this interfacial composition is thatit exhibits improved tensile strength, elongation, modulus ofelasticity, adhesive properties, and electrical characteristics which inmany instances exceed the properties of individual organic componentspresently employed in the art.

BRIEF DESCRIPTION OF THE DRAWING The advantages of the instant inventionwill become apparent upon consideration of the following disclosure ofthe invention, especially when taken in conjunction with theaccompanying drawing wherein:

The FIGURE represents a schematic illustration of one embodiment of axerographic member as contemplated for use in the instant invention.

DETAILED DESCRIPTION OF THE DRAWINGS In the drawing, reference characterillustrates one embodiment of an improved photoreceptor device of theinstant device. Reference character 11 designates a support member whichis preferably an electrically conductive material. The support maycomprise a conventional metal such as nickel, nickel alloys, brass,aluminum, steel or the like. The support may also be of any convenientthickness, rigid or flexible and in any suitable form such as a sheet,web, cylinder, or the like. The support may comprise other materialssuch as metalized paper, plastic sheets covered with a thin coating ofaluminum or copper iodide, or glass coated with a thin conductive layerof chromium or tin oxide. A preferred substrate for use in the instantinvention comprises a seamless flexible xerographic belt which comprisesa metal such as nickel, nickel alloys or brass, and which is formed bythe method described in Applicants copending application, Ser. No. 7,289filed on Jan. 30, i970, now abandoned.

Substrate 11 is overlayed with an organic interfacial layer 12, whichcomprises a polymer blend or mixture of a polycarbonate,polyether-ester-urethane and chlorosulfonated polyethylene. Thepolycarbonate may be present in a concentration of from about 30 to 80weight percent with the two elastomers comprising a combinedconcentration from about to 70 weight percent. Preferably thepolycarbonate should be present in an amount from about 70 to 80 weightpercent. The polyether-ester-urethane and chlorosulfonated polyethyleneare preferably present in a combined concentration of about 10 to 30weight percent. Interfaces which comprise a polymer blend of the abovethree components have been found to exhibit particularly outstandingelectrical and mechanical properties at both extremes of operationtemperatures (20 to 100F) and therefore comprise a desirable interfacialmaterial for use in xerography.

Typical polycarbonates suitable for use in the instant inventioncomprise Merlon polycarbonate available from Mobay; Makrolonpolycarbonate available from Bayer; and Lexan polycarbonate availablefrom General Electric.

Typical polyether-ester-urethanes suitable for use in the instantinvention comprise Estane 5702 F-2 available from Goodrich and TPUpolyurethane available from Goodyear.

Typical chlorosulfonated polyethylenes suitable for use in the instantinvention comprise Hyperlon 30 or Hyperlon 20 available from duPont.

The interfacial layer may be made by any convenient technique. Forexample, the appropriate proportions of the polycarbonate and elastomersare normally dissolved in a solvent and the solution coated onto asupporting substrate. The solvent is then allowed to evaporate leaving adried coating contained on the supporting substrate. Residual solventsmay be driven off by oven drying at to 300F for about 5 minutes. Typicalcoating techniques which are suitable for forming the interfacial layerinclude spray coating, draw coating, dip coating or flow coating. ingeneral, the dried thickness of the interfacial layer should be about0.5 to 3.0 microns. Thicknesses less than about 0.5 microns areundesirable in that they do not give a uniformly cover substrateroughness. In addition, they are difficult to charge and tend to leakelectrical charge. Thicknesses above about 3.0 microns sometimes resultin non-charge dissipation. in general, the composite resistivity ofthese interfacial layers range from about l0 to l0 ohm-cm.

In addition to the above compositions. other additives may be added tothe mixture. These additives include small amounts of conductive orphotoconductive pigments such as copper phthalocyanine, zinc oxide(electrography grade), cadmium sulfoselenide, and metal-freephthalocyanine. In general these additives are used to control theresistivity of the interfacial barrier layer, and in some cases are evenbelieved to improve the mechanical properties of layer.

Although the exact structure of the interface is not completelyunderstood, it is believed that the elastomeric polymers form a discretedispersed phase in a polycarbonate matrix. It is also believed that itis essential to form such a discrete phase by agitating the polymericsolution prior to its application in the form of the interfacial layer.At concentrations of the elastomeric phase greater than about 35 weightpercent, it is believed that this two phase structure begins to undergoa phase inversion and the desired properties both electrical andmechanical are drastically different after the phase inversion. Forexample, the elongation reaches a minimum in the phase inversion region,and the resistivity increases steeply in or around the phase inversionregion.

It has also been found that when many organic resins are used alone asinterfacial layers, the desirable combination of mechanical andelectrical properties cannot be maintained. For example, polycarbonatealone is not a suitable barrier layer in that its resistivity is toohigh. Similarly, many elastomeric materials when used alone also do notyield the desired combination of mechanical and electrical properties.For example, interfacial layers comprising polyurethane alone do nothave the required mechanical properties such as high modulus ofelasticity and therefore are not suitable as interfaces for flexiblexerographic photoreceptors when used alone. Similarly, interfaciallayers comprising chlorosulfonated polyethylene alone also do not yieldthe required mechanical properties with regard to high modulus ofelasticity. Electrically, these elastomers alone are somewhat tooconductive, but the con ductivities are greatly reduced by theincorporation of the high resisitivity polymers in the matrix.

A preferred application of the instant invention includes the use of theinstant interface on a flexible seamless belt which may typicallycomprise a conductive material such as nickel, nickel alloys or brass.In addition to the required electrical characteristics, it is essentialthat the interfacial layers of the instant invention have a high degreeof flexibility at extremes of application temperature and forms asatisfactory adhesive interface between the photoconductive layer andthe supporting substrate.

Photoconductive insulating layer 13 overlays interfacial layer 12, Thephotoconductor may comprise any suitable photoconductive insulator whichis compatible with the composition of the interfacial layer and forms anadherent layer which properly bonds the photoconductive layer to thesubstrate. Suitable photoconductive materials include vitreous seleniumor selenium alloyed with materials such as arsenic, antimony, tellurium,sulfur, bismuth and mixtures thereof. A preferred photoconductorcomprises a vitreous alloy of selenium containing arsenic in an amountfrom about 0.1 to 50 percent by weight. The thickness of thephotoreceptor layer is not particularly critical and may range fromabout ID to 200 microns. In general, thicknesses in the range from about20 to 80 microns are particularly satisfactory for use in conventionalxerography. The photoreceptor layer may be prepared by any suitabletechnique. A preferred technique includes vacuum evaporation wherein theappropriate material or alloy is evaporated over the interfacial layer.In general, a selenium or selenium-arsenic alloy layer thickness ofabout 60 microns is obtained when vacuum evaporation is continued forabout 1 hour at a vacuum of Torr. at a crucible temperature of about280C. US. Pat. Nos. 2,803,542 to Ullrich; 2,822,300 to Mayer et al,290M348 to Dessauer et al and 2,753,278 to Bixby all illustrating WWWevaporation techniques which are suitable iii the formation of seleniumor selenium alloy layers of the instant invention.

In order to gain added sensitivity when using selenium-arsenic layers, ahalogen dopant such as chlorine or iodine, may be added in order toimprove the electrical characteristics. This concept is more fullydescribed by US. Pat. No. 3,3l2,548 to Straughan.

PREFERRED EMBODIMENTS The following examples further specifically definethe present invention with respect to a method of making a photoreceptormember having an interfacial barrier layer. The percentages in thespecification, examples and claims are by weight unless otherwisestated. The examples below are intended to illustrate various preferredembodiments of the instant invention.

EXAMPLE I The coating solution for forming organic interfacial barrierlayer is prepared by dissolving equal proportions by weight (1:l:l) of apolycarbonate resin, an amorphous polyether-ester-urethane elastomer andchlorosulfonate polyethylene as follows:

Part A-polymer 6 parts by weight ethylene dichloride-I00 partsdioxane-IOO parts The above coating solution is further diluted asfollows:

Part B-(Part A 250 parts by volume) cyclohexanone (100 parts by volume)tetrachloroethylene I00 parts by volume) This coating solution is coatedonto a continuous flexible nickel belt .0045 inches thick approximatelyl6 /2 inches wide and 65 inches in circumference by spray coating usingan air spray in a Binks electrostatic spray gun. The coating is allowedto dry and forms a smooth interfacial film about 1 to 2 microns inthickness. The coated nickel substrate is then mounted on a circularmandrel and then inserted into a vacuum chamber. An alloy sourcecontaining about 99.67 weight percent selenium and .33 weight percentarsenic and containing 30 parts per million chlorine is inserted in astainless steel crucible beneath the coated nickel substrate. Duringvacuum evaporation the substrate is rotated about its longitudinal axisat a rate of about 6 to 12 revolutions per minute. The vacuum chamber isevacuated to a vacuum of about 5X10" Torr. The crucible contained in theselenium-arsenic alloy is then heated to a temperature of about 300C andevaporation continued for about 40 minutes resulting in the formation ofa 50 micron vitreous selenium-arsenic alloy photoconductive layer beingcoated over the interfacial barrier layer.

EXAMPLE II The photoreceptor belt member made by Example I iselectrically tested as follows: The belt is mounted on a tri-rollerassembly adapted to rotate the belt over each roller. A corotroncharging device is located at a point along the path of travel of thebelt and a 15 watt cool white erase lamp is located at a point 0.25inches from the charging unit. The belts are tested for electricalcharge acceptance by charging to a potential of about 900 volts. Thecharge is then erased by exposure to the erase lamp. The charging andexposure cycle is carried out I00 times with the dark discharge beingmeasured after the first cycle. The initial charge acceptance after thefirst cycle is 870 volts; the charge acceptance after the 100th cyclewas 920 volts. The residual voltage was 40 volts and the contrastpotential available for development was 880 volts. The dark dischargeafter the first cycle was 2 percent. These electrical properties aredeemed acceptable for commercial xerographic photoreceptor.

Before and after forming the photoconductive layer, the interface andphotoconductive selenium alloy were subjected to a scratch test. Thistest is conducted to determine the degree of adhesion of the interfaciallayer to the substrate and the degree of adhesion of the selenium layerto the interfacial layer. This test is conducted by hand by scraping apronged metallic device over the surface of the appropriate layer. Bothlayers exhibited good adhesion when subjected to this test.

The belt of Example I is also subjected to a cold test to determineadhesion and resistance to cracking at low temperature. The belt iswrapped in aluminum foil and placed in an ice chest filled with ice for24 hours. After 24 hours, the selenium layer remained intact with noevidence of cracking or spalling away from the interface.

Although specific components and proportions have been stated above inthe above description of the preferred embodiments of this invention,other suitable procedures and materials such as those listed above, mayalso be used with similar results.

Other modifications and ramifications of the present invention wouldappear to those skilled in the art upon reading the disclosure. Theseare also intended to be within the scope of this invention.

What is claimed is:

1. A xerographic member which comprises a conductive substrate havingthereon an interfacial barrier layer having a thickness of about 0.5 to3.0 microns, said barrier layer comprising a polymer blend or mixture ofa polycarbonate, a polyether-ester-urethane, and a chlorosulfonatedpolyethylene, with the polycarbonate being present in a concentration ofabout 30 to weight percent and the poly-urethane and chlorosulfonatedpolyethylene being present in a combined concentration of about 20 to 70weight percent, with said interfacial layer having a compositeresistivity of about l to 1O ohm-cm, and a photoconductive layer aboutto 200 microns in thickness overlaying said interfacial layer.

2. The member of claim 1 in which the photoconductor comprises avitreous alloy of selenium and arsenic.

3. The member of claim 1 in which the arsenic is present in an amount ofabout 0.1 to about 50 percent by weight with the balance substantiallyselenium.

4. The member of claim 1 in which the photoconductive layer comprisesabout 99.67 weight percent selenium and 0.33 weight percent arsenic.

5. The member of claim 4 in which the seleniumarsenic photoconductorcontains a chlorine dopant.

6. The member of claim 1 in which the photoconductive layer comprisesvitreous selenium.

7. The member of claim 1 in which the photoreceptor member is in theform of an endless flexible belt.

8. The member of claim 7 in which the flexible belt substrate is made ofnickel.

9. The member of claim 7 in which the belt substrate is made of brass.

10. The member of claim 7 in which the belt substrate is made of amaterial selected from the group consisting of nickel, brass, aluminumand stainless steel.

11. The member of claim 8 in which the photoreceptor comprises about99.67 weight percent selenium and 0.33 weight percent arsenic.

12. The member of claim 11 in which the seleniumarsenic photoconductorcontains a chlorine dopant.

1. A XEROGRAPHIC MEMBER WHICH COMPRISES A CONDUCTIVE SUBSTRATE HAVINGTHEREON AN INTERFACIAL BARRIER LAYER HAVING A THICKNESS OF ABOUT 0.5 TO3.0 MICRONS, SAID BARRIER LAYER COMPRISING A POLYMER BLEND OR MIXTURE OFA POLYCARBONATE, A POLYETHER-ESTER-URETHANE, AND A CHLOROSLULFONATEDPOLYETHYLENE, WITH THE POLYCARBONATE BEING PRESENT IN A CONCENTRATION OFABOUT 30 TO 80 WEIGHT PERCENT AND THE POLY-URETHANE AND CHLOROSULFONATEDPOLYETHYLENE BEING PRESENT IN A COMBINED CONCENTRATION OF ABOUT 20 TO 70WEIGHT PERCENT, WITH SAID INTERFACIAL LAYER HAVING A COMPOSITERESISTIVITY OF ABOUT 10**11 10**14 OHM-CM, AND A PHOTOCONDUCTIVE LAYERABOUT 10 TO 200 MICRONS IN THICKNESS OVERLAYING SAID INTERFACIAL LAYER.2. The member of claim 1 in which the photoconductor comprises avitreous alloy of selenium and arsenic.
 3. The member of claim 1 inwhich the arsenic is present in an amount of about 0.1 to about 50percent by weight with the balance substantially selenium.
 4. The memberof claim 1 in which the photoconductive layer comprises about 99.67weight percent selenium and 0.33 weight percent arsenic.
 5. The memberof claim 4 in which the selenium-arsenic photoconductor contains achlorine dopant.
 6. The member of claim 1 in which the photoconductivelayer comprises vitreous selenium.
 7. The member of claim 1 in which thephotoreceptor member is in the form of an endless flexible belt.
 8. Themember of claim 7 in which the flexible belt substrate is made ofnickel.
 9. The member of claim 7 in which the belt substrate is made ofbrass.
 10. The member of claim 7 in which the belt substrate is made ofa material selected from the group consisting of nickel, brass, aluminumand stainless steel.
 11. The member of claim 8 in which thephotoreceptor comprises about 99.67 weight percent selenium and 0.33weight percent arsenic.
 12. The member of claim 11 in which theselenium-arsenic photoconductor contains a chlorine dopant.